1. Central Neural Mechanisms Involved in Coupling between Respiratory and Masticatory Activities of TonguePremotor neurons projecting to hypoglossal motoneurons were found among respiratory neurons recorded from the medullary reticular formation in pentobarbital-anesthetized cats. (1) Some of them responded with antidromic spikes to stimulation of both the hypoglossal and phrenic motor nuclei.(2) The somata of these neurons were double-stained antidromically with a fluorescent dye (Fast blue) injected into the hypoglossal nucleus and another fluorescent dye (Nuclear yellow) injected into the phrenic motor nucleus. (3) Spike-triggered averaging of the efferent discharges in both the hypoglossal and phrenic nerves by spontaneous spikes of these neurons revealed that the discharges in both the hypoglossal and phrenic nerves were facilitated after a monosynaptic latency from the triggering spikes. The results indicate that the axons of some medullary respiratory neurons bifurcate to innerv
… Moreate both hypoglossal and phrenic motoneurons. It was concluded that these hypoglossal excitatory premotor neurons projecting to both the hypoglossal and phrenic motoneurons were involved in coupling between respiratory and masticatory activities of the tongue.2. Central Neural Mechanisms Involved in Switching between Respiratory and Swallowing Activities of TongueRespiratory movements stop coincidentally with swallowing, and tongue activity switches from the respiratory rhythmic pattern to the swallowing pattern. To study the roles of the medullary respiratory neurons described above in switching of tongue activity from respiration to swallowing, single unit activity was recorded from the hypoglossal premotor neurons showing respiratory activity in chloralose-anesthetized, bilaterally-vagotomized and immobilized cats. It was found that the inspiratory neurons projecting only to the hypoglossal motoneurons showed burst activity coincidentally with swallowing evoked by electrical stimulation of the superior laryngeal nerve, while those projecting to both the hypoglossal and phrenic motoneurons stopped firing during the swallowing. It was concluded that these changes in activity of the hypoglossal excitatory premotor neurons in the medullary reticular formation were involved in switching of tongue activity from respiration to swallowing. Less